The present invention generally relates to call delivery in a wireless network. More particularly, and not by way of limitation, the present invention is directed to a system and method for routing a call request to an Internet Protocol Multimedia Subsystem (IMS) network for a Mobile Directory Number (MDN) homed on a network switch in a second generation (2G) wireless network.
FIG. 1 shows an exemplary wireless network architecture 10 to implement the existing call delivery solution using Wireless Intelligent Network (WIN) operations. The network architecture 10 in FIG. 1 shows a wireless operator (or carrier) network 12 providing wireless communication facility to deliver a call origination request to a subscriber 14 that has an IMS subscription. In the discussion herein, the reference numeral “14” is used interchangeably to refer to a “subscriber” or a subscriber's mobile device or terminal. A base station (which may be part of a Radio Access Network (RAN)) 16 may provide the air interface to the mobile terminal 14 to facilitate wireless communication with the terminal 14. The operator network 12 may also include a call switching or routing network 18 including a network switch (e.g., a Mobile Switching Center (MSC)) 20, a Home Location Register (HLR), and a WIN Service Control Point (SCP) 24. Various network elements in the switching network 18 may have circuit-switched connections therebetween. The MSC functionality may be divided so that the call control or mobility management and routing function may be implemented using a Mobile Switching Center emulation (MSCe), whereas the bearer resources may be supported using a Media Gateway (MGW) or an MGW Media Resource Function Processor (MGW-MRFP) (not shown). Because of the focus of the present discussion on the routing aspects in the network 12, the reference numeral “20” is used to refer to the MSCe as the network switch in the operator network 12 for the sake of simplicity and ease of discussion. As is known, the HLR 22 may contain a database (not shown) for storing subscriber-specific information such as, for example, the subscriber's Mobile Equipment Identifier (MEID), the subscriber's Mobile Directory Number (MDN), the address of the subscriber's “home” or “registered” location, the class of services subscribed by the subscriber, etc. The WIN SCP 24 may provide service control functionality through routing support as discussed later with reference to FIG. 2.
The carrier network 12 may be a wireless network such as a Time Division Multiple Access (TDMA) based network, a Code Division Multiple Access (CDMA) network, or a cdma2000® network.
The network switch 20 may be in communication with a wireline network 25 (e.g., a Public Switched Telephone Network (PSTN), a Public Land Mobile Network (PLMN), or an Integrated Services Digital Network (ISDN)) to receive the calls for the subscriber 14 routed through the wireline network 25. For ease of discussion below, the term “PSTN” is primarily used with the reference numeral “25” while describing the call delivery mechanisms with reference to FIGS. 2 through 5.
The network switch 20 also may be in communication with an IP Multimedia Subsystem (IMS) network 26, which may be deployed by the operator of the wireless network 12 to provide support for multimedia services (e.g., texting, audio-visual content delivery, Internet or website access, etc.) to the subscribers in the network 12. Thus, in the network topology of FIG. 1, the IMS-capable subscriber terminal 14 may access the IMS network 26 through the base station 16. Although the IMS network 26 is shown as a part of the operator's wireless network 12, such IMS network 26 may be a separate network associated with the wireless network 12, or the IMS network 26 may be in another operator's network. The IMS network may provide multimedia sessions between an end-user terminal (e.g., the MS 14) and PSTN 25 or between PSTN 25 and Internet Protocol (IP) multimedia servers and content providers (not shown). The IMS network 26 may support multimedia sessions using the Session Initiation Protocol (SIP) and Session Description Protocol (SDP) to set up and control calls/sessions. Several roles of SIP servers or proxies, collectively called Call Session Control Functions (CSCF), may be used in the IMS network 26 to process SIP signaling packets in the IMS network 26. Thus, the IMS network 26 may include an Interrogating Call Session Control Function (I-CSCF) 28 as an “entry point” or “point of contact” located at the edge of the network 26. The I-CSCF 28 may receive a call (e.g., a voice and/or a data call) in the form of a SIP request routed thereto from the MSCe 20 (as discussed below with reference to FIG. 2), and may query a Home Subscriber Server (HSS) 30 to retrieve the address of a Serving-CSCF (S-CSCF) 32 and assign it to the IMS user (e.g., the subscriber 14) performing an IMS registration. The I-CSCF 28 may also forward SIP requests and responses to the S-CSCF 32. The I-CSCF 28 can also be used to “hide” the internal IMS network from the outside world. The HSS 30 may be a database that supports the IMS network entities (e.g., I-CSCF, S-CSCF) that actually handle calls. The HSS 30 may contain the subscription-related information or the subscriber profile, may perform subscriber authentication, and may provide information about the subscriber's location and IP information. The S-CSCF 32 may be a SIP server performing session control. The S-CSCF 32 may download user profiles or subscriber profiles from the HSS 30 to decide which IMS application server (not shown) should receive user's SIP messages to provide the multimedia services the user is authorized to receive. The S-CSCF 32 may also provide necessary routing services and enforce the policy of the network operator. It is understood that, contrary to the switching network 18, the IMS network 26 may be a packet-switched network (having packet-switched connections between various network elements therein).
The IMS network 26 may be coupled to another packet-switched network 34 (e.g., an Internet Protocol (IP) network such as the Internet) as well as a circuit-switched network (not shown) (such as the PSTN) to accomplish the desired connections beyond the carrier network 12. As shown in FIG. 1, the IMS network 26 may also be coupled to a Radio Access Network 16 to establish a connection to subscriber 14. Thus, as discussed below with reference to FIG. 2, a PSTN-originated call request may be re-routed to the subscriber terminal 14 via the IMS network 26.
When the subscriber 14 subscribes to mobile voice service, the operator of the wireless network 12 assigns the subscriber 14 (i.e., the subscriber's mobile handset or terminal) a Mobile Directory number (MDN) (which assists the network in routing calls to the subscriber terminal 14). The wireless network operator will then “home” (or register) the MDN on a network switch—here, the MSCe 20. This implies that all calls directed to the subscriber 14 and routed through the PSTN 25 to the subscriber's MDN will be routed to the subscriber's “home” MSCe (i.e., the MSCe 20) for service and further processing. It is noted here that the MDN may be an International Telecommunication Union Telecommunication Standardization Sector (ITU-T) E.164 number (having up to 15 digits) in accordance with the International Telecommunication Union's (ITU) international numbering plan for PSTNs in which each assigned number contains a country code (CC), a national destination code (NDC), and a subscriber number (SN). Once the MDN has been assigned to the MSCe 20 and the PSTN's network element router tables (not shown) are updated to route calls placed to the MDN to that MSCe 20, it may be difficult for a network operator to re-home the MDN to another network element within its network.
As new multimedia services are deployed, wireless network operators desire the freedom to route the call request from an MSCe into a multimedia network (e.g., an IMS network). If a subscriber subscribes to multimedia services and has not yet been assigned an MDN, then the wireless network operator will home the new MDN assigned to the subscriber to a network element within the multimedia network—i.e., the IMS network. However, if the subscriber has already been assigned an MDN (which is homed at an MSCe) and desires to add multimedia service to their subscription, the network operator will most probably leave the MDN homed on the MSCe. In this case, it is easier for the network operator to deploy a re-routing mechanism from the MSCe to the multimedia network (i.e., the IMS network) than to update the PSTN network element router tables.
FIG. 2 illustrates operations among various network elements in FIG. 1 to accomplish call delivery to an entry point (or entry element) for the IMS network 26—here, the I-CSCF 28. In FIG. 2, the originating operation is indicated by capital letters (e.g., LOCREQ), whereas its response operation is distinguished by using lower case letters (e.g., locreq) so as to maintain conciseness while depicting operations/messaging among various network elements without writing each operation by its full form. The operational sequence 36 in FIG. 2 may be as follows:
1) Initially, at step 38, the MSCe 20 receives a Call Origination from the PSTN 25. The Call Origination request may have originated from another wireline or wireless device (not shown), a service provider entity (e.g., a specific multimedia server), etc. The PSTN 25 routes the Call Origination request to the MSCe 20 with the MDN in the Called Party Number (CdPN) element of the Call Origination request because this MDN is homed at the MSCe 20.
2) At step 40, the MSCe 20 sends an American National Standards Institute-41 (ANSI-41) Mobile Application Part (MAP) Location Request (LOCREQ) INVOKE to the HLR 22 containing the CdPN (=MDN) received in step 38 in the Digits (Dialed) (alternatively referred to herein as “Dialed Digits”) parameter of the MAP LOCREQ INVOKE.
3) At step 42, the HLR 22 responds with an ANSI-41 MAP LOCREQ RETURN RESULT (concisely indicated as MAP: locreq [ . . . ] in FIG. 2) to the MSCe 20. If the subscriber 14 has subscribed to IMS services, the LOCREQ RETURN RESULT instructs the MSCe 20 to perform an AnalyzedInformation (ANLYZD) WIN operation to the WIN SCP address provided in the LOCREQ RETURN RESULT operation.
4) At step 44, the MSCe 20 sends an ANSI-41 MAP ANLYZD INVOKE to the WIN SCP 24 containing the MDN received in step 38.
5) Based upon the received MDN value, the WIN SCP 24 constructs or maps the MDN to a routing number. The routing number may be combination of the MDN and a set of additional digits. It is noted here that different MDN values could be assigned different sets of additional digits. For example if MDN=800-555-xxxx, then the routing number could be 1234-800-555-xxxx, whereas if MDN=800-333-xxxx, then the routing number could be 6789-800-333-xxx. At step 46, the WIN SCP 24 responds with an ANSI-41 MAP ANLYZD RETURN RESULT (concisely indicated as MAP: anlyzd [ . . . ] in FIG. 2) to the MSCe 20 containing the routing number.
6) Through internal translations, the MSCe 20 uses the routing number (from the WIN SCP 24) to determine that the MSCe 20 is to send a SIP INVITE to an IP address of the next hop (e.g., the I-CSCF 28). At step 48, the MSCe 20 sends a SIP INVITE to the next hop or entry point (here, the I-CSCF 28) for the IMS network 26 with a Telephone Universal Resource Identifier (TEL URI) in the SIP INVITE set to the MDN.
It is noted here that in the case where the wireless network operator had assigned a new MDN to the subscriber for IMS services or had decided to take the onerous step of updating the network routing information (i.e., PSTN network element router tables), the Call Origination (from the PSTN) may have been routed by the PSTN directly to an IMS entry element (e.g., a Media Gateway Control Function (MGCF)) (not shown) instead of through the MSCe 20 as shown in FIG. 2. However, because of an operator's preference for MSCe-based re-routing—especially in case of an already-assigned MDNs, the network architecture for such direct communication to an IMS entry element is not shown in FIG. 1, nor is such communication shown in FIG. 2